I'm growing my Arums in a sandy mix. I grow A.
italicum, maculatum, dioscorides, nigrum, orientale, Dracunculus vulgaris in it.
The Dutch grown Dracunculus doesn't like it at all, but the wildly collected one
Formula as folows:
1600 dm3 coarse sand
1000 dm3 black turf
500 dm3 perlite, Ø 0-1 mm.
For base ferilization 0,5 kg KCl in autumn, and
about 12 dm3 old manure for 10 m2. Than harmonic
fertilizer is added in the same dosage in summer (16:16:16).
Peter Boyce told me A. dioscorides and Dracunculus
vulgaris grows together in SW-Turkey, so this mix must be good for both of them,
if they were collected in the wild.